A generally employed ionizer applies high voltage to a needle electrode for generating ions by focusing the field to a top end of the needle electrode. The focusing of the electric field to the top end of the needle electrode is so intense that the top end of the electrode is likely to be deteriorated, thus degrading the performance for a long-term use.
As the needle electrode has a narrow ion generation region, the resultant ion generation amount is small. The ion generation amount may be increased by raising the voltage. However, the electric field at the top end of the needle electrode becomes so intense that generation of ozone with strong oxidative power is facilitated.
Patent Document, Japanese Unexamined Patent Application Publication No. 10-189282, discloses the ionizer for generating ions on a circumferential surface of the conductive wire to which high voltage has been applied for the purpose of solving the aforementioned problem of the needle electrode. The above-described ionizer is of AC type for generating positive and negative ions alternately by applying AC voltage to a single wire as the electrode. The use of such ionizer for generating the positive and negative ions using the single electrode causes the negative ion to have the same ionic concentration as that of the positive ion at lower voltage. When employing the aforementioned ionizer for alternately applying the positive and the negative voltages at the same level to the single wire electrode, generation amounts of the positive and the negative ions become different, thus disturbing the balance of the generated ions. The adjustment device for adjusting the positive and negative voltages is required to be added to the high voltage generator circuit for the purpose of realizing the good ionic balance by adjusting the ion generation amount. The positive ion generation amount may be increased by raising the positive voltage through the aforementioned adjustment. However, this may cause the problem resulting from the intense electric field around the electrode owing to the high voltage.